This invention relates to a three-phase induction motor control method in which the output is controlled so as to be constant by sensing fluctuations in power supply voltage.
Recent control of three-phase induction motors is in many cases performed through either of the following methods:
(1) a method of controlling the frequency and voltage of the motor power supply by an inverter, or PA1 (2) a vector control method of controlling the instantaneous value of motor stator current and generating a torque equivalent to that of a shunt DC machine.
Since the output of an induction motor generally varies in proportion to the square of the voltage impressed upon the motor, the output will fluctuate when the AC input voltage undergoes a large variation, irrespective of whether the inverter method or vector control method is employed. Countermeasures devised in order to prevent such a fluctuation in output include varying inverter control pulse widths in dependence upon the AC input voltage in the inverter method and varying the amount of maximum slip in dependence upon the AC input voltage in the vector control method. Nevertheless, satisfactory results are not obtained in terms of holding the output of the induction motor constant.